PlatSil® 71-40 and RTV-4140 are both Shore A40 platinum-cure silicones, placing them in a relatively firm range for reusable mold making. This hardness can help reduce mold deformation during casting and handling, although greater rigidity can make deep undercuts and complex demolding more demanding.
The mixing systems are significantly different. Polytek specifies a 1A:10B ratio by weight for PlatSil® 71-40, while RTV-4140 uses a 1:1 ratio by weight or volume. The 1:1 system can simplify routine batch preparation, whereas the 10:1 system requires more precise component measurement.
Working and cure times also create a clear processing difference. PlatSil® 71-40 has a published 90-minute pour time and approximately 24-hour demold time, while RTV-4140 has approximately 35 minutes of working time and a 6-hour published cure time. PlatSil® 71-40 therefore provides a longer working window, while RTV-4140 offers a shorter published turnaround.
Viscosity should be interpreted carefully. Polytek reports approximately 38,000 cP for mixed PlatSil® 71-40, while MinghuiLink reports approximately 4,800±200 mPa·s for Part A of RTV-4140. Because these values refer to different measurement points, they should not be treated as a direct like-for-like laboratory comparison. Actual flow, air release and pouring behavior should be evaluated with the intended mold design.
The published mechanical data show different performance profiles. RTV-4140 reports higher published tensile and tear strength, while PlatSil® 71-40 reports higher elongation. These values should be treated as published reference figures rather than a strict laboratory ranking because the manufacturers may use different test methods and conditions. PlatSil® 71-40 also has documented brush-on adaptability when used with PlatThix Liquid Thickener or fumed silica, providing an additional mold-making option beyond conventional poured molds.
